Valentina was an aide to the royal court in Nimbus Land prior to the game's beginning. After Prince Mallow disappeared, Valentina locked King Nimbus and Queen Nimbus in a room in the palace. Valentina then lied to the townsfolk, saying that the king is sick and may die soon. She also sent her minions to guard the palace as well as the beanstalks leading up to the clouds where Nimbus Land lies, and fired much of the royal staff. As a final precaution, Valentina instructed Shy Away to block the pipe leading to Nimbus Land by causing Smilax to grow in it.

Valentina's next plan was in motion as Mario, Mallow and their friends arrived in Nimbus Land, having overwhelmed Shy Away's Smilax minions as well as the enemies guarding the beanstalks. Valentina passed off her enormous, avian assistant Dodo as the lost Prince Mallow. For some reason, the townsfolk bought it. Dodo then "proposed" to Valentina, legally making her queen. The two then returned to the palace. Having learned the truth about Mallow's heritage from Garro, Mario covered in gold snuck into the palace, disguised as a statue. Valentina enjoyed the statue and put it on display, but Mario soon starts to chase her. Valentina returned to the Nimbus Land plaza, but her lies were beginning to come to light. Mario soon arrived, and with her plan in pieces, Valentina engaged the hero in battle.

At the beginning of the battle, Valentina calls Dodo to carry away the middle party member. That member must then fight Dodo alone. When Dodo is damaged to a certain degree, the bird retreats, the ally giving chase, and the battle returns to Valentina. Valentina uses a wide array of magic but is physically frail. After a while, Dodo and the kidnapped party member return. and Mario and his friends prevail. The duo then retreats, leaving behind the key required to rescue Mallow's parents. After this, her minions disappear from the castle, as well as several statues of her being replaced with King Nimbus ones.

After being defeated, Valentina and Dodo flee Nimbus Land, and find refuge in Booster's Tower, where Valentina was courted by the maniacal Booster. In a scene viewable if the player climbs to the top of the Tower again, Valentina refuses Booster's request to marry her. Booster then whispered something in her ear, causing the usurper queen to fall in love with him, though Booster seems to have cold feet about the new relationship. The pair is wed in Marrymore at the game's end with Dodo acting as the priest, but for an unknown reason, Booster freaks out and flees the church, a surprised Valentina pursuing him.

Valentina has been shown to be an extremely bossy and domineering person who seems to treat her henchmen and just about everyone else around her with as little respect as possible. Despite the blatant disrespect she shows toward her underlings (especially towards Dodo), as well as the apparent hatred they have toward her (as shown in Birdy's Psychopath), they still remain loyal to her regardless. Valentina is also arrogant and vain. This is shown when she thinks highly of herself, believing herself to be beautiful beyond compare, as well as a refined "art buff."

Valentina appears as a pale skinned woman who wears a white dress, which moves during her battle. She has a parrot on her head and red shoes. During her battle she carries a martini glass which has no effect on the gameplay.